Synchronizing system



3 Sheets-Sheet 2 INVENTOR LeSZerJWQZ I A'TTORNEY L. J. WOLF Filed Dec.

Nov. 11, 1930.

SYNCHRONIZING SYSTEM Nov. 11, 1930.. L. J. WOLF SYNCHRONI ZING SYSTEM 3 Sheets-Sheet 3 -i g INVENTOR Lester]. W0!

l atentecl Nov. 1 1,l9"30 UNETEDSATES P TENT oFFICE.

1' 8; MANUFACTURING COMPANY, A CORPORATIONOE PENNSYLVANIA sYNoHRoNIzI G SYSTEM Application filed December 9, 1927. Serial No. 238,823.

' My invention relates to radio broadcasting and particularly to the problemof maintaining. two separated broadcasting stations at the same wave length.

An operator using a receiving set placed at a distance from each of two broadcasting stations sending the 3 same program may choose from which station he will get the program by tuning to the wave length of one or the other station. The effects of fading often interfere more effectually with the reception from one broadcasting station than from another. If the two broadcasting sta-. tions workon the same wave length thesignal will be received fromthat station which is least affected by the fading and the listener will hear it without knowing or caring from which broadcasting station it arrived.

7 If the advantage of two separated broadcasting stations working on the same wave length is to be obtained, the wave lengths must be exactly equal, otherwise there will be a beat-note in the receiving set which ordinarily will completely spoil the reception of the signals. Any means for maintaining the wavelengths at two broadcasting stations alike will fail to accomplish useful results unless theflequality of the wave length is maintained with great accuracy. A very small percentage change in the wavelength at one station will be suflicient to produce a perceptible beat-note in any receiving set which is within reach of both stations. a

Attempts made heretofore to maintain two produce a low frequency at eachstationto maintain said low frequencies equalby control impulses transmitted from one station to the other and to produce, at each station,

from the low frequency there a frequency capable of radiation. In this way, I can maintain the two radiationfrequencies equal.

If an oscillating system be provided with.

regenerative arrangements, that is, with meanswhereby the energy delivered by the system ationeipomt is made to control, the

supply of energy to the system at another.

point, the manner in which the system will LESTER J. WOLF, OF SOUTH BEND, INDIANA, ,ASSIG NOR TQ WESTINGHOUSE ELECTRIC oscillate is dependent on the degreeof regeneration, if the regeneration is not large enough to overcome the damping, the oscillations will die away. If it is almost but not quite enough to completely counteract the damping, the rate of decay of the oscillations will be small and the system will continue in oscillation for some time after the stimulus which caused the oscillations has ceased. Theoretically, it is possibleto provide a degree of regeneration which would just compensate for the damping and the system then would, if set into oscillation, continue tooscillate at a constant amplitude. If the regeneration be greater than this, the oscillations will increase in amplitude, and, if the regeneration be sufliciently great, the oscillations will start from such insignificant stimuli that they are called spontaneous.

I have discovered that it is possible to control the frequency of the oscillations provided the desired frequency does not differ much from the natural frequency of the re generative system and provided further that the degree of regeneration is properly It is an object of my in entionto apply I this discovery to the control of the frequency of a remote broadcasting station.

It is a further object of my invention to provide at one broadcasting station a mechanically oscillating system maintained in oscillation by regenerative arrangements, and to provide at a remote broadcasting station an oscillating system supplied with a regenerating'arrangement adjusted, as explained above, to such a degree of'regeneration that the frequency may be controlled by impulses from the first mentioned broadcasting station.

It is a furtherobject of my invention to 'oonveyhthe frequency-controlling impulses from the mechanically oscillatinagisystem in one station to that in the other by means of a modulation impressed upon a carrier tire quency.

It is a further obj'e'ct'of m inventi n-t ,provi dethe aid carrier frequency; by developi-ng from the said mechanically oscillating system. I

a further object of this invention "to develop from the same mechanically oscillating system, a suitable frequency for the broadcastingcarrier wave. I

Other objects of th's invention "and details 6f the construction will 'be apparent from v isenip loyed as a source of mechanical frequencj'y, having a natural period such as the following description and the acco .pa-nying drawings, in which:

Figure 1 is a diagram of the circuits and apparatus involved; I a Fig. 2 is a diagram of the circuits associated with the, mechanically oscillating systern at the controlled station;

Fig. '3 is a diagram of the circuits and apparatus employed for multiplying the frequency. r

At the sending station, a tuning fork 1 qu'ency. Other sources of mechanical 'frep'endulu ms, watch balance wheels constant pressure turbines; centrifugal governors and "the like, may beused instead ofa tuning rork if desired. Piezoelectric crystals also are suitable Ifort'his ur ose. a V Upon one tine of the fork'l, the coil 2 is provided which is connected to theinput of amplifier 3. The output of the amplifier is connected to the winding of a magnet 4: associated with the othertine of the fork. Preferably, a member 5 of magnetic material is located between the "free ends of the '-;t1nes.

T he output 'of the amplifier 3 is also connected to a modulator 6 by means of which the oscillationsdeveloped in -an oscillation generator 7 are modulated in accordance with the movement of the fork. The oscillations are delivered to. an antenna; 8 by a which they are broadcast.

The output of the amplifier is' also delivered to a frequency multiplier which is caused to control the frequency ofanoscillator 11. The oscillatorniaybe merely a power amplifier connected with the last tube of the-frequency multiplier. The outputof l theoscillator is delivered to anantenna 12 from which the signalis broadcast.

The radiation d elivered'by the antenna 8 is received'upon an antenna J15 near the remote broadcasting station. Any suitable receiving set 16 produces from these oscillations a currentcorresponding to the modu- {lati'on thereof, that is a. currentcorrespond- .ing to the movenien'tof thefork 1f The current is amplified by the amplifier 17 and impressed upon a line 18 by-whichitis-conveyed' over a short distance jtoftheremote broadcasting station. It is then impressed upon a filter 19 through which it isdelivered to. an amplifier 2O and,'after' passing.

through a filter 21; is impressed upon a driving magnet 22 of a fork 23. The fork 23 is as nearly equal in; frequency to the forkl as can be conveniently; provided.

nected. The output coil 241s also connected to a frequency multiplier 30 which controls the. oscillator in thesaine ,way that the frequency multiplier 10 controls the oscillator 11, the oscillator 31 delivers energyto the antenna 32 from which the broadcasting action is radiated. I

V The signal originates at the microphone "35 which is located in astudio or at the scene of'the'program to be broadcast; This may he remote from one or 'both of the broadcastmg stations. U

The signal is amplified by amplifier S6 and is impressed upon the line 37; A filter 38.

at one end of this line connects the line to the "modulator 139, by which the outputof the oscillator 11 is modulated. The line 37 is also connectedthrough a filter il to the modulator 42 which modulatesthe output of the 'osci ldator 3l. The signals impressed upon the microphone 35, are thus reproduced as modulationsupon the energy broadcast from the antennae '12 a and 32. s I

I The set 16upon which the en ergy radiated from' the antenna 8'is received is of any desired or suitable type. For example, t is convenient to' have in the aparat'us lG-both a receiver of .the'ne'utroyne type and areceiverof the superhetero V dyn'e type with arrangements for switching from 'oneto the other, whereby that onemay i V be selected which is best adapted to the con Menace ditions prevailing at the time. When two different receiving sets are used'it is prac ticalto use the same amplifier 17 for either 'is' thus conveniently correlated with the imtube 51 is connected to the input of the tube pedance of the filter 19 and amplifier 20. A connection 47 ,Fig. 2, to the midpoint of the primary of the transformer 45 iscontrolled by a signal device such as the key 48 by means of which the switching arrangements at" the receiver 16 may be manipulated. If

'. desired, the arrangements in the station at antenna may include signalling devices. The key 48 then affords means for communication between the remote broadcasting station at antenna 32 a'ndthe receiving substation at antenna 15.

The output of thefilter 19 is connected to the amplifier 20 which, as illustrated in Fig. 2, comprises two portions, one portion being between the filter 19 and the tube 26 and the other portion being between the tube 26 and the driving magnet associated with the fork.

As illustrated in Fig. 2,the first portion of the amplifier 20 includes two tubes and 51 arranged incascade. The output of the 52 which is the first tube of the second portion of the amplifier. This portion. also comprises a plurality52, 53 of tubes arranged in cascade. The connection between the two portions comprises a link circuit 54.

uniting the output transformer 55 of the tube 51 with the input transformer 56 of the tube52ju a The connection from the output coil 24 5-. ofthe fork 23 to the amplifier is 'made by 1 the wayof this link circuit. The connection includes a potentiometer 57 comprising a resistor connected across the terminals of the'coil 24. Oneterminal ofthe resistor is connected through a grid-biasing device 60 to the commonconductor for the filaments of the tubes. The adustable contactor of the potentiometer 57 is connected to the grid of the tube 26. i

The tube 26 is resistancecoupled to the input of the transformer 56, this coupling comprising the resistor 61 and the condenser 62. a The coupling is completed by theconnection 63 between the link circuit and the T common conduct-or for the filaments.

The output circuit from the tube 53, at the exit of the amplifier 20, is connected to the magnet'22 through a phase-control device.

1 As illustrated, the phase-control device is a high-pass filter including condensers 65 and 66 in series, with an inductor 67 in shunt. The filter is so designed thatitscut-olf frequency is close to the naturalfrequency of the fork 23, consequently, small changes in the value of the inductance in the filter will cause relatively large changes in the phase of the currentin the magnet 22.

A portion of the inductor the plate-filament space of the tube 68. The conductivity of this space is controlled b the grid, which is connected through the grid-biasing device 60 to the common con- 67 is shunted by ductor for the filaments. The device 60 affords anadjustable potential and the shunting effect of thetube 68 upon the inductor 67 is controlled by adjustment of said po- .tential. i a

The frequency multipliers indicated at 10 i and 30 in Fig. 1 may be of any desired type,

but the type illustrated in Fig. 3 is preferred. The conductors 71 extend from the coil 24 in Fig. 2 to the input of the first tube ,7 2 of the frequency multiplier. The tube 72 the drawing byshowing a heavy iron core for the inductor 76.

resonant circuit in the plate circuit of the 5 I The other paralleltube 73 includes acondenser 77 and an inductor 78, which together form a parallelresonant circuit for the frequency of a harmonic of the inputto the tube 73. The grid of the tube 79 is connected to the point 80 between the two parallel-resonant circuits in the plate circuit of the tube 73. u

Thecircuit 7 5-7 6 offers a very large impedance to the fundamental frequency, and only a small impedance to the harmonic frequency,while the circuit 77-78 offers a very large impedance to the harmonic frequency andbut little impedance to the fundamental frequency. Consequently, the voltage impressed upon the grid of the tube 79 isalmost entirely of the harmonic frequency.

In an embodiment of this invention which has been placed in practical operation,the

cores than the transformer in the amplifier including tubes 72 and 73.

Similarly the output circuit of the tube 84 contains two parallel-resonant circuits, one 85 being resonantto the fundamental frequency of the input of the tube 84 and the other 86 being tuned to a harmonic there of. In the practical embodiment mentioned above,.-the natural period of the circuit 86 is seven times that ofthecircuit 85., The

7 tube -89 isrelated-t the tube 8a in a way analogous to. the relation of thetube 79to the-tube' 'l'g'and the tube 8.91s thefirst-o f a pair of. tubes 89 and 90v forming an amplifier which is adapted totransmit the frequency of i the circuit 86. i The transformer in this amplifier is, therefore, designed for even a higher frequency and its core-should have little or no iron.. parallel-resonant circuit 92 t med to the; same frequency a'sthe circuit 86 and-a parallelresonant circuit 93 tuned to a harmonicthereaof In the embodiment mentioned'abovdthenatural period of the circuit 93 is seven times that of the circuit 92. The tube-:95 is related to tube 90 in a manner similar tothat in Which tube 7 9 is related to the tube 73; vThe tube '95 therefore, amplifies. a frequency higher than anyof'the preceding. tubes. It is connected to-the nexttube by a radio-frequency choke coil 96 and a-condenser 97. r

' Thetube to which the condenser 9'? is con".

nected is the power tube of the oscillator 31,

Fig, 1. Itmay be a singlepower tube ora battery of power'tubes arranged in parallel .as desired. v V. -i

The natural frequency of the. fork 23 is; maintained'asnearly constant as possible. Inorder to accomplish thisthe fork is encased ina housing 100 of heat-insulating material,

for example. a Wooden box. Within the housmg; a lamp 10l is provided'to,maintainthe boX-ata higher temperature than its. surroundings. v

- A second lamp 102' preferably smaller than thelainplOl is located outside the casing. at any pointconvenient for observation. For

example, it may. be mounted upon the top of a-box. v The circuit for-the lamps is connected to any suitable constantsource of power A thermostatic circuit controller 103 situated Within thebox 100 establishes a shunt about the lamp .102 whenever the-box is cool and opens said shunt upon-sufficient rise of tern-- iperaturewlthin the box. \Vhenthe shunt .1s estabhsheda larger current flows through visions for maintaining a constant frequency.

' 'Inthe operation of thedevice, supplying energy to the amplifier 3 in Fig; 1 sets the fork 1 into vibration. The movement ofthe tines toward each other causes an increase in thefiux through the coil 2 and the movement of them away from each other causes a. dim].-

nution of thefluX in the coil 2'.l-The changes in: flux produce ohangesin the electromotive The outputyof the circuit 90 includes a force delivered by the coil 2 to theamplifier 8. The action .of this amplifierv impresses f upon the magnet lcurrent which is atthe same frequency as the output from the coil 2. The fork is thus maintained inzoscillation. j j i The body 5 of magnetic material-between the tines prevents the fork from vibrating like a pendulum about its-standard, Such movement Would-cause" the right handtine to approachthe body'5 while the left handtine recedesfrom it. ,One air gap is, therefore, decreasing at the time, the other air gap is increasing. Theresultantchange in flux, is, therefore, either zenoor-very small. On. the other-hand, wherethe b11168" approach each other both air. gaps; become shortand 7 when thetines rec'ede from each: other both air gaps become long; Marked changes. in flux are thus causedfl The regenerative connection through the-amplifier 3 is thus. effectire for the usual motion of the fork and'ineffective for the pendulum-like motion. 7

The frequency generated by'the fork is impressedupon the frequency multiplier 10- and multiplied by 'it. The resultant. high fre quency is further amplified by the oscillator 11 and impressed upon-the antenna- 12. lnt'he embodiment of the system referred toabove, 1

thenatural frequency of the fork 1 is only sii ghtly less than 4000 cycles-per second. {The multiplying; action of; the frequency multi-. plierlO in said embodiment-is of themagnitude stated in connection with Fig. 3 and-consequently produces a. total multiplication by 14?, giving for the frequency in theantenna l2 some1570 kilocycl'es. a The oscillation generator 7 may be con:-

trolled infrequency-by a similar frequency multiplier governed byt-he same fork 1, but

this is not necessary. A 1y source of high frequency oscillations-"Willserve for this os- 'cillat'o'rlz- The frequency chosenin the embodiment mentioned above corresponds-to a wave length of some 65'. meters. The 65- of; the -fork,;somewhat less than 4000 cycles. This modulated 65-1Il8t61 radiation is re-. ceived upon'the antenna 15' Whichin the above mentioned embodiment is somethou- 0 lio' meter rad ation1s-modulatedat'theirequency sand miles from theantenna Sand: aboutone mile from the antenna32.

Y The receiving set lozproducesfr'omthe energy receivedupo'n'the antenna 1'5jan output current of about 4000 cycles, that is, of a fre quency. corresponding exactly. to the frequency of the fork 1.

V The receiv ngset may beadjustedbyan attendant stationed near the antenna 15, but

this is not ,alwaysnecessary. The receiving 7 set may be controlled from thestat'ion at the antenna. 32 by manipulating'thekey 48-. Any

suitable switching orremote-control device may be associated withthe receiving'set 16 to enable the operator at thebroadcasting stament ofthereceiving set 16, at the antenna 15..

tionriat the antenna 32 to control the adjust- Theamplifier .17 atthe receiving station increases theforlnfrequency current to a value transmitted readily over the lineld which longenough to. permit the antenna to be well separatedfrom the antennac32 but not long enough to cause serious difiiculty in transnrtting current of this frequency.

Intheabove embodimenuit is abouta mile long. The filter-191s a lngh-pass-hlter. It

is designed notgonly tozcompensate for the i tenuation' in the line- 18 butto prevent extraneous frequencies-whichjmay have entered JThe current offfork from the filter 19 is amplified by. both portheline 18 from being impressed on the amplifier20. .Thefrequency delivered by the fil-. ter. 19 "is the frequency of the. fork l. The transformer and the output transformer of.

tionsof the amplifier 20 and then impressed upon the driving magnet 22. .In the construction illustratedwin .Fig. 2, the second part of the amplifier20 acts as the regenerating. amplifierfor the fork 23. It is not,

however, necessary that the amplifier for regenerating the fork 23 shall beaportion of the amplifier which increases the current deliveredfronix the filter19. Ifthese two amplifiers are separate it is possible to ad just one without disturbing the adjustment circumstances.

of the other whichhas advantages in some When the amplifier, which. forms ti er:

tion'of this regenerativeconnection, is separated from theamplifier'which cooperates. with the filter 19, the degree of regeneration maybe adjusted without altering the degree of amplification applied-t0 the'impulses received from thereceiving setw16. In this way, it is possiblefoivarythe ratio between thetwo sources of energyacting upon the fork. It is desirable ,thatithe impulses re ceived from the receiving set shall have a control control The ma gnet .22, because the current which it receives is .ofJthe frequency determined by the fork 1, impresses ,uponthe; fork im- I pulses which correspond nearly to the natu-...

ral frequency; ofthis fork.

interaction of the tines and the magnetic member 25 inducesin the coil 24L, explained j ered by the amplifier 20 and the currentln in connection with the" fork .1, an electromo tive force of the same frequency. 1 ea The electromotive force from the coil 24: is

- impressed across the grid and filament of I the tube 26. Adjustment of the potentiometer57 will serve to regulatethemagnitude of the felectro'motive force I delivered to the grid of the tube 26. The-outputof the tube thatlthe regeneration in the system, comprisnatural periodof; the system can be adjusted greatly exceeding the regenerative The fork 23 is thus set intovibration. j The y the magnet 22. i

. coil 24: to the magne1'w22. .For example,it

26 is impressed through the condenser 62 and the transformer 56 upon the input of the j tube 52. It is then amplified by the righthand "portion of the amplifierQO and so impresses upon the magnet 22 a current which serves to assist in keepingthc fork 23in 0scillation. a i j i The adjustment of the potentiometer 57 and the design of the amplifier are so chosenv ingfork 23, coil 24, amplifying system and magnet 22, is between the degree which wills prevent rapid dampingand thedegree stated hereinafter. Moreover, the. natural frequency of the fork 23 differs: but slightly from the frequency delivered by the transformer 55 to the system. As explained be. low, the system includes means whereby the and so. made even closer to the period ofthe current from the line18. i i w i The forks 1 and 28. are so constructed as:

to have as nearly as possible the same natural period. In addition to this,*thep forks are maintained at very nearly the same temperature. The small difference in frequency, which remains after these precautions are all taken,isremovedl almost completely by: an adjustment of the phase relation between i theoutput of the amplifier 20 and the cur- "rent in the magnet 22. .Ihave found it possible by the adjustment of this phase to, change the period of oscillationof the system including the fork. 23, the regenerating tube 26, the; amplifier tubes .52 and 53 and? the magnet 22 by as much as five cycles where the natural period oflthe fork 23fis inthe neighborhood of 4000 cycles. If desired a similar provision for adjusting thefork frequencymay be provided at the, fork 1. r i

The adjustment of thephase relation is accomplished by adjusting the biasing potential upon the gridofthetube .68. r This. changes the internal impedance ofthe tube68 and thereby alters the effectiveness with j and thus results in a slight alteration of the;

cut-ofi' frequencyof the. filter comprising? condensers 65 and 66 and inductor 67 This filter is so designed that its cut-ofi frequency is very nearly equal to the natural frequency 1 ofthe fork 23. Consequently, a very small change in. the inductance will result inwa veryconsiderable changein the phase relation between the electromotiveforce deIiV-J:

. Any phase-changing device be used 5 instead of thejfilterjustdescribed, although I have found such a filter preferable. .Also

i the phase-changing device may be locatedat anypoint in the regenerative system from the 11o which it shunts a portion of the. 1nduc-tor67;

25 the tadingpersists.

I may bevinserted between the coil '24 and the' atmospheric conditions between the antenna 8 and the antenna 15." Fading may cause these impulsesto become so small that they canno longer produce perceptible effect. m When this occurs, the .tork 23 will cont1nue to oscill ate because of-the regenerative-icons nectionthrough the tube'26 to' 'the magnetQ-EZL It the degree of regenerationfi-s :onlyyeryi' slightly less than the damping, the "tor-k "will;

1y ZQQIIlQ tO rest, but it is quitepossible torso adjust the regeneration that-the perIo'dsre-Q I quired for the :fork to come'to rest islon ger than the time during} which any rd'inary ta'l'ing will cause the impulsestromithe rreceiving set to be ineffective. Tlrisf tendenoy of the :torktopersist iIlfVlbIffltlOIl, :"thus is a means :tori keeping the broadcasting station at the properirequency duringitheitime that;

-With a properly chosenzdegree of regenera ti'on, it is possible to control the frequency of thetork 23 by *the frequency ot the impulses from the filter I9. For this purpose {there must be sufficient regeneration to :ensurethat u 'p on cessation of impulses from the #filter 1%) the motion of the forh'vvi l'l d ie out ion'ly very 'sloWly,-i{ at;all. A q It. the regeneration be too greatytor ex l 351 ample if it cause asvoltage at the magnet 22 greater than the yoltage caused there by the impulseslfrom the receivingset 1'6, suehcon- T trol is not'po'ssible. J 3

The control can be obtained with any de;

440;; gree of regeneration, between these limi ts jif' the frequency of the impulses tromith'e frilter 1 9fl87 suflioiently close to the frequency o fithe' regenerative system; When these 'ftrequ'en c'i'es are very nearly equal, the control 9f the 51 frequency 'o't the fork by theirequenfoy fo f'f the e The systemther'etore atfords a" meanston y, ea imaintarniiig the frequency'at the antenna 32 impulses =fro1nr the =filter will continue to be effective as the impulses become smaller until they become much smaller th an would "be required to reestablish such controlfonce the fork has reverted to *the natural lt're'opuen'oy "of f the regenerative system.

When the; impulses from the filter-become too-feeble to control the" fork, the latter" changes to the frequency of the regenerative '1 esgsystem and Whenthe-i-mpulses tromfthefilter again become of; sufiicient strength to 'establis'h-control, the fork frequency c'hang'esf'to; that ot the/impulses. V Y

equal to the frequency v at -the antenna 12 even when large fading efiects o'ccur between ani 1 teninae *8 and l5 andzeven When the fading prevents fill GOIII'HILlIlIOfilElOIl between-these V 1 T-'.jantenn etomseveralseconds atIaj-time; I v

Static efilectslas Well astading effects cause changes in the output from the receiving; set

These static effects are very largely eliminated by the filter 19. The Tfilter therefore serves thedouble purpose of correcting the selective attenuation of the line 18 and} eliminating'to a large eXtentthe-static impulses. r

The static impulses which'are not elimi- I nated byfthe'filter aresomewhat amplified by slowly diminish its amplitude and may'linaih the 'fork l; gonsequently these static impulses are Without perceptible eliec't upon lVloreoverjif it should happen that a suncession of static impulses, resembling closely enough the regular impulses from the "fork P1,

should arrive :at the amplifier 20, their efi'ect upon theiinoiveinent of the tori: would "be only temporary; ,As soon iastherstaiticaimpulsesare everzor cease to silnulate'the con trolling uiinpulsesfthe controlling impulses would :bring the regeneratirve system includ ingrthe' auras back to-the lrequency ofthe 'i ocr'kl." The impulses received from zt-he :Eorik' 11 through thecoil2:andtheiimpulseslreceived over the line 71 from il'ilTiCOll 524E,- ener gilze d Eby thefork :23; :are' multiplied" frequency and imp're'ssedupon fthe respectiveian tennae-bythe transmitterssets Hand :31; a l The multiplying device is il lus'tra tedzin Fig. 3.; Thevlow frequency-currents received from the torlr areamplifiedto' such extent thatthe output er the last arnpli fierythetube 73 :as illustrated5 is highly "distorted." "This distortion will be the cause of numerous han monies. Because the tuned circtiit" Z5-TF6 is paralle'l-reson ant; to the fundamental, elm

potential'oli 'fundamental frequency man lbe largely absorbed :th ls ci-rcuit The point] 1 80," therefore, will receive only very small! potential changes ot {this frequency. 1 58ecause'fthe parallel-resonant circuit tuned to the frequency of the selectedlliarmonic, the potential-of the frequencychanges between the point *8'0 and the filaments will} c be :large, flout potential 'cha-ngesoif Erie};

Consequently, the oteiitiali'imjposed the grid oftube'79 Wil'l bealmost-entirely of l the frequency oftheselected harmonic. This frequencyjin its turn isamplified and a simii.

lar action-by the-circuits 85 "and 86 will irn lress a hi 'herfharmonic uponthe grid otthei tube 89. "Thisin' 'its turn Willi-be multiplied by the parallel-resonantcircuits 92 and "93, producing upon the grid of the tube-96. f potential changes" of "a frequency sulficientily high to serve for the transmitting :ot theigantennariTh s:lirequency is delivered over the condenser 97, to the oscillator 31 and,

transmission. lar and SImLIltaIlGOIlS VELIlELtlODS 1n intenslty If fading causes the in the case of the multiplier 10 over a similar condenser, tolthe oscillator 11. In this way, radio-frequency oscillations of the same frequency are produced in the two antennae.

The signals from the microphone are transmitted over the line 37 to both broadcasting stations. The filters 41 and 38 are designed to correct the selective attenuating action of the lines. The energy impressed upon the modulators 39 and 42, therefore, is

of a quality nearly unaffected by the line These modulators cause simiat the two broadcasting stations.

Consequently, any receiving set located within the reach of both stations will receive the same signalupon the same wave length modulated in the same Way from either station or from both stations simultaneously.

signal from one broadflcasting station to disappear altogether, the signal from the other broadcasting station jso ' will continue to operate the receiving set, the

listener will be unaware of any effect due to the fading.

The regenerative constant-frequency generator disclosed in this application is dcscribed and claimed in my copending applieation Serial No.,238,824, filed December 9,

1 927, and assigned to theWestinghouse Electric & Manufacturing Company.

. Although I have described in detail but a singleembodiment of my invention and have mentioned only a few modifications thereof, it'will be evident to those skilled in the art I that manyother modifications are possible and I, therefore, do not intend any limitation, except such as is required by the prior art or stated in the claims.

a I claim as my invention:

$1.1m a radio system, a broadcasting station, a second broadcasting station remote "therefrom, means for maintaining said stations at the samecarrier frequency comprisan osclllating system at one station and a ing regenerative oscillatory system stimulated thereby at the other station.

-2. In a radio system, a broadcasting stat tion, a second broadcasting station remote therefrom, means for maintaining said stations at the same carrier frequency comprising an oscillating system atone station and a regeneratlve oscillatory system stlmulated 5 thereby at the other station, the degree of regeneration being sufficientto cause the regenerative systemto continue in'oscillation after stimulation thereof has become ineffective for at leastas long a time as fading can ordinarily render said stimulation ineffective.

'- 3. In a radio system, abroadc-asting station, a second broadcasting station remote therefrom, means for maintaining said stations'at the same carrier frequency comprising an oscillating system at one statlon and a. regenerative oscillatory system stimulated thereby at the other station, the degree of regenerationbeing sufficient tocause there:

generative system to. continue in oscillation after stimulation thereof has. become ineffective for at leastas long a time as fading can ordinarily render said. stimulation ineffective, and insufficient to cause said regener ative system to build up oscillations large compared with saidstimulation.

4. In a radio system, a broadcasting station, a second broadcasting station remote therefrom, means for maintaining: said stations at the same carrier frequency comprising an oscillating system at one station and a regenerative oscillatory system stimulated thereby at the other station and high frequency oscillations one at each station each controlled by the said oscillating system at.

its station.

5. In a radio system, a broadcasting station,a second broadcasting station remote therefrom, means for maintaining said stations at the same carrier frequency compris- 111g an oscillating system at one statlon and a regenerative oscillatory system stimulated thereby at the other station, frequency multipliers of like multiplying power associated respectively with said oscillating systems, and high-frequency oscillators governed by said frequency multipliers, whereby the high frequency at each station is the same multiple of the frequency of the said oscillating system at one station. i

6. In a radio system, a broadcasting station, a second broadcasting station remote therefrom,1means for maintaining said stations at the same carrier frequency comprising an oscillating system at one station and a regenerative oscillatory system stimulated thereby at the other station, frequency multipliers of like multiplying power associated respectively with said oscillating systems and, highrequency oscillators governed by said frequency multipliers, whereby the high frequency at each station is the same multiple of the frequency of the said oscillating system at one station, a source of signals, modulators, one at each station, for the respective high-frequency oscillators there and I a communication channel connecting said source of signals to each modulator, whereby the broadcasting from each station is on the same carrier Wave length modulated in the same way. a

7. In a frequency control system a frequency-determining device including a member having a characteristic period of To I mechanical oscillation, a second frequencydetermining device including a member havmg a characteristic period of mechanicaloscillatlon of approximately the same magn1- tude as the first-mentioned member, means includinga thermionic tube for adjusting the a frequency determined by the first-mentioned 

